Steering pinion

ABSTRACT

A steering pinion ( 1 ) manufactured with finished toothing by cold or hot forming in the form of a one-piece coupling linkage between steering shaft ( 6 ) and rack ( 4 ) of a steering mechanism on a motor vehicle, wherein the steering pinion ( 1 ) is provided with a cylindrical toothed portion ( 3 ) having helical toothing on its outside and with a collinearly adjoining cylindrical journal portion, whose diameter is larger than that of the toothed portion and whose end portion contains a driver recess for connection of the steering shaft ( 6 ). A transition region between the root circle of the helical toothing and the journal portion ( 2 ) comprises at least two conical portions, namely a radially outer conical portion having a first cone angle (α 1 ) (die angle), which is disposed between the tip diameter at the toothing end of the helical toothing and the journal portion ( 2 ), and a radially inner conical portion having a second cone angle (α 2 ) (entrance angle) , which is disposed between the tip diameter at the toothing end and the root circle of the helical toothing.

The invention relates to a steering pinion manufactured with finishedtoothing by cold or hot forming in the form of a one-piece couplinglinkage between steering shaft and rack of a steering mechanism on amotor vehicle, wherein the steering pinion is provided with acylindrical toothed portion having helical toothing on its outside andwith a collinearly adjoining cylindrical journal portion, whose diameteris larger than that of the toothed portion and whose end portioncontains a driver recess for connection of the steering shaft, andwherein a transition region is provided between the root circle of thehelical toothing and the journal portion.

Steering pinions of this type are described in Japanese Patents 7-308729A and 11-10274 A. For control of material flow during forging, theyprovide an approximately triangular face, which is disposed within thehollow mold of the forging die in the entry region of the toothingflights. This triangular face is inclined in such a way that it expandsthe entry region and also sets the material flow in rotation, so thatbetter filling of the mold cavities forming the helical toothing isachieved. In connection with these known proposed solutions, a problemthat has not yet been considered is that, despite good filling of thecavity for the toothed member, uniform filling of the cavity for thejournal portion is not assured, especially if a driver recess having alarge area compared with the outside diameter of the journal portion isprovided.

In contrast to the foregoing, the object of the present invention is toprovide a geometry of the steering pinion such that the correspondingcavity of the die used for forming favors material flow in two oppositedirections, namely for filling the cylindrical toothed portion on theone hand and the collinearly adjoining journal portion of the steeringpinion on the other hand.

The shaping of the steering pinion with which this object is achieved isevident from the body of claim 1 of the present invention. According tothat claim it is provided that the transition region between the rootcircle of the helical toothing and the journal portion of largerdiameter comprises at least two conical portions, namely a radiallyouter conical portion having a first cone angle α₁ (die angle), whichextends between the tip diameter at the toothing end of the helicaltoothing and the journal portion, and a radially inner conical portionhaving a second cone angle α₂ (entrance angle), which extends betweenthe tip diameter at the toothing end and the root circle of the helicaltoothing, that the die angle α₁ is larger than or equal to the entranceangle α₂ and that the transition region describes at least one roundedportion having a first radius R1, which bridges between the outerconical portion and the cylindrical outside surface of the journalportion.

Such a design of the steering pinion ensures that the flow resistanceduring forming of the said pinion can be controlled in such a way bysuitable choice of die angle α₁ and entrance angle α₂ that completefilling of the die cavities is ensured. For use of the inventiveteaching, the resistance during pressure application can be adjustedsuch that the material of the blank flows in the two opposite directionsin a manner matched to one another. In this connection, it is apreferred objective that, during complete filling of the journalportion, the elongated flights of the helical toothing also becompletely filled out in the region of the toothed portion. An importantfact in connection with the present invention is that, by suitablechoice of the inlet resistance into the toothed portion, the material ispressed in the opposite direction with generation of an adequateback-pressure. Thereby there can be achieved flawless filling of thejournal portion even in the case of a driver recess of relatively largedimensions.

According to an inventive proposal, it is provided that the die angle α₁is determined in such a way as a function of the cross section of thedriver recess that, relative to the outside diameter of the journalportion, it increases or decreases in the same sense with the dimensionof the cross section of the driver recess. Thus, if the cross-sectionalratio between driver recess and journal portion is increased, it will bepreferable to choose a correspondingly larger die angle α₁.

For dimensioning of the entrance angle α₂, it is provided according tothe invention that this will be determined in such a way as a functionof the helix angle β of the helical toothing that it increases ordecreases in the opposite sense with a change in helix angle β. In thisway the influence of helix angle β on flow resistance is balanced out,thus making it possible to match the material flow toward the toothingwith that in the opposite direction, or in other words toward thejournal portion.

Within the scope of the invention, there can be provided, besides theouter conical portion and the inner conical portion as well as therounded portion with a first radius R1, still further rounded portions,so that smooth transitions for steady material flow are assured. In thiscontext, there is preferably provided a rounded portion with a secondradius R2, which forms the transition between the outer and innerconical portions. Furthermore, there can be provided another roundedportion with a third radius R3, which bridges between the inner conicalportion and the root circle of the helical toothing. In this way thereis produced a quasi-transition region with a turning point at the heightof the tip diameter at the toothing end, provided the entrance angle α₂is smaller than the die angle α₁. The two conical portions lie on a lineonly when the two angles are equal. Starting from the rule underlyingthe inventive teaching, to the effect that α₁ is greater than or equalto α₂, it is found in the case of unequal angles that the radii R1 andR2 are curved in opposite direction. Radius R3 has the same direction ofcurvature as radius R2. For radius R3, therefore, the same situation asfor radius R2 applies in regard to R1, meaning that radii R1 and R3 arecurved in opposite directions.

It is self evident for the person skilled in the art that, from the formof the steering pinion defined in the claims according to the presentinvention, there is automatically obtained a corresponding hollow moldof the die for the forming process. As an alternative to cold extrusion,forming can also be accomplished by forging.

The inventive steering pinion will be described hereinafter withreference to the drawing, wherein

FIG. 1 shows a three-dimensional diagram of the steering pinion,

FIG. 2 shows a partly cutaway side view of the steering pinion,

FIG. 3 shows a cross section III-III according to FIG. 2, with a driverrecess in the form of a profile having two faces,

FIG. 3 a shows an alternative version of FIG. 3, with a driver recess inthe form of a hexagonal profile,

FIG. 3 b shows an alternative version of FIG. 3, with a driver recess inthe form of a spline,

FIG. 4 shows a schematic diagram of the transition region betweenjournal portion and toothed portion, and

FIG. 5 shows an enlarged side view in perspective.

FIG. 1 shows a three-dimensional diagram of an inventive steering pinion1. It has a cylindrical journal portion 2 and, in the collinearextension thereof, a toothed portion 3, which is also cylindrical andwhich has a twisted or helical toothing that extends over its entirelength. With steering pinion 1 there is associated, as illustrated by abroken outline, a rack 4 for a steering mechanism in a motor vehicle,the said rack having a toothed section 5. In a finished steeringmechanism, the helical toothing of steering pinion 1 engages in rack 4and displaces it according to the steering deflection, which istransmitted via the steering column of the vehicle to a steering shaft6, illustrated as a broken outline. At its end next to steering pinion1, steering shaft 6 has two oppositely disposed flats 7, which form keyfaces for coupling with a driver recess 9—not visible in FIG. 1 butshown in FIGS. 2 and 3 of the drawing—in the end of journal portion 2next to the steering shaft. At its coupling end, moreover, steeringshaft 6 has a cylindrical centering projection 8, which is inserted intoa corresponding bore 11 (FIG. 2) in the center of driver recess 9 (FIG.2). Bore 11 can be made either by forming or by subsequent machining bya chip-removing method.

In the side view according to FIG. 2, driver recess 9 is illustrated inthe region of journal portion 2. By means of bounding lines 10, FIG. 3shows a flat contact face 18, against which there bear key faces 7 ofsteering shaft 6 almost without play, as well as a bore 11 for receivingcentering pin 8 of steering shaft 6. The helical toothing of toothedportion 3 of steering pinion 1 is illustrated schematically in thestandard form, wherein broken line 12 corresponds to the root circle ofthe toothing and envelope line 13 to the tip circle. At the inner end oftoothed portion 3 there is indicated, between lines 15 and 16,transition region 14 between the cylindrical part of journal portion 2and toothed portion 3 as well as circumferential line 17, which denotesthe toothing end.

FIG. 3 corresponds to section plane III-III in FIG. 2. It shows therelatively large cross-sectional area—illustrated without brokenoutlines—of driver recess 9, contact faces 18 for lateral key faces 7 ofsteering shaft 6, and central bore 11.

FIGS. 3 a and 3 b show alternatives to FIG. 3. Specifically, FIG. 3 ashows a driver recess whose key faces are formed by a hexagon profile,and FIG. 3 b shows a driver recess formed as a kind of internal spline.

FIG. 4 schematically illustrates the principle of the inventivesolution. It is a diagram of steering pinion 1 in transition region 14as a half section through longitudinal axis 19. In order to establishthe relationship to FIG. 2, the boundaries of transition region 14 asdefined by upper line 15 and lower line 16 are illustrated. The heightof upper line 15 is defined by the transition between radius R1 and thecylindrical outside surface of journal portion 2. Lower bounding line 16is defined by the transition of radius R3 to root diameter 12. Alsoshown is envelope line 13—which corresponds to the tip diameter of thetoothing—of toothed portion 3. Hereinafter an explanation will be givenof the significance of four further horizontal lines 21 to 24, which runparallel to bounding lines 15, 16 of transition region 14, namely withinthe said region. They are used for a detailed description of thetransition region as defined in claim 1.

Together with the contour of the transition region, line 21 generates anintersection point 31 in the transition between the curvature accordingto radius R1 and a radially outer conical portion 25, whose cone angleis denoted as die angle α₁. The height of line 22 is defined byintersection point 32 between the inner end of outer conical portion 25and radius R2, which runs through envelope line 13 corresponding to thetip diameter of toothed portion 3 and forms the transition to a radiallyinner conical portion 26. Intersection point 33 between radius R2 andradially inner conical portion 26 defines the height of line 23. Theradially inner end of inner conical portion 26 is marked by intersectionpoint 34 on line 24. Starting from intersection point 34, radius R3,which is curved in the same direction as radius R2, forms the transitionto envelope line 12, which corresponds to the root diameter of thetoothing. Together with envelope line 12, line 16, which boundstransition region 14 within toothed portion 3, generates intersectionpoint 35, which forms the end point of the contour of transition region14. In this way there is defined a transition region 14, composed of twoconical portions 25, 26 and three radii R1, R2, R3. Of those, onlyradius R1, which bridges the large change in diameter between journalportion 2 and toothed portion 3, is important. It is entirelyconceivable that radii R2 and R3 can be omitted, especially if die angleα₁ and entrance angle α₂ do not differ greatly from one another. In sucha case, intersection points 32 and 33 migrate to positions above oneanother, and so they eventually become located on envelope line 13corresponding to tip circle 13 of the toothing, and intersection point34 migrates to a position above intersection point 35 on adjacentbounding line 16 of transition region 14.

Assuming the direction of material flow for filling toothed portion 3during cold extrusion is the direction indicated by arrow 27, outerconical portion 25 means that the inlet resistance increases with thevalue of die angle α₁. Only if this resistance zone is overcome does theentrance angle α₂, which is usually smaller, determine the further flowresistance of the material during filling of the hollow mold forming thehelical toothing. The smaller the value chosen for entrance angle α₂,the more rapidly is toothed portion 3 filled. However, it must be notedhere that entrance angle α₂ depends on helix angle β of the helicaltoothing (see FIG. 5), specifically in such a way that entrance angle α₂increases or decreases in the opposite sense of a change in helix angleβ. Thus an increase of helix angle β is compensated for by a smallerentrance angle α₂, whereby the entrance resistance decreases, and viceversa.

FIG. 5 is an enlarged diagram showing the helical toothing in the regionof toothed portion 3 as well as helix angle β. Lines 15 and 16 boundtransition region 14 in accordance with the definition explained withreference to FIGS. 2 and 4. Line 28 denotes the end of the helicaltoothing next to journal portion 2. Radially outer conical portion 25runs between lines 21 and 22.

To the shape of the hollow mold of the die in the entry region oftoothed portion 3 there corresponds the approximately triangular face29, which corresponds to radially inner conical portion 26, whoseinclination is defined by entrance angle α₂. This triangular shape 29forms the bridge between the entrance region and the actual helicaltoothing.

1. A steering pinion (1) manufactured with finished toothing by cold or hot forming in the form of a one-piece coupling linkage between steering shaft (6) and rack (4) of a steering mechanism on a motor vehicle, wherein the steering pinion (1) is provided with a cylindrical toothed portion (3) having helical toothing on its outside and with a collinearly adjoining cylindrical journal portion, whose diameter is larger than that of the toothed portion and whose end portion contains a driver recess (9) for connection of the steering shaft (6), and wherein a transition region (14) is provided between the root circle (12) of the helical toothing and the journal portion (2), characterized in that the transition region (14) comprises at least two conical portions, namely a radially outer conical portion (25) having a first cone angle (α₁) (die angle), which is disposed between the tip diameter (13) at the toothing end of the helical toothing and the journal portion (2), and a radially inner conical portion (26) having a second cone angle (α₂) (entrance angle) , which is disposed between the tip diameter (13) at the toothing end and the root circle (12) of the helical toothing, in that the die angle (α₁) is larger than or equal to the entrance angle (α₂) and in that the transition region (14) describes at least one rounded portion having a first radius (R1), which bridges between the outer conical portion (25) and the cylindrical outside surface of the journal portion (2).
 2. A steering pinion according to claim 1, characterized in that the die angle (α₁) is determined in such a way as a function of the hollow cross section of the driver recess (9) that, relative to the outside diameter of the journal portion (2), it (α₁) increases or decreases in the same sense with the dimension of the cross section of the driver recess.
 3. A steering pinion according to claim 1, characterized in that the entrance angle (α₂) is determined in such a way as a function of the helix angle (β) of the helical toothing that it (α₂) increases or decreases in the opposite sense with a change in the helix angle.
 4. A steering pinion according to claim 1, characterized in that the transition region (14) describes a rounded portion having a second radius (R2), which forms the transition between the outer conical portion (25) and the inner conical portion (26).
 5. A steering pinion according to claim 1, characterized in that the transition region (14) describes a rounded portion having a third radius (R3), which bridges between the inner conical portion (26) and the root circle (12) of the helical toothing. 